Assembling nano-objects into macroscopic arrays is required for many applications including biomaterial sensing, photonics, plasmonics and quantum information processing. Several top down assembly methods, including lithography or dip-pen techniques, as well as bottom up methods using patterned self-assembled monolayers or electrostatic self-assembly have been developed. While these methods are capable of high resolution patterning of nano-object arrays, the assembled components are only weakly bonded to the substrate and therefore cannot undergo further processing, such as wet chemistry processing steps (e.g., sonication) or subsequent lithography. Such further processing is often required for device applications where the nano-objects act as active components in microfluidic devices, as sensing probes or photon sources in which they are coupled to plasmonic structures or other optical elements.
Nano-objects are useful for sensing of bio-molecules by selective adsorption of bio-molecules to functionalized surfaces. Gold is typically chosen as a substrate for biosensing due to its inertness relative to biological systems and its ability to form sulfhydryl- or thiol-terminated surfaces (—SH). These thiol groups may spontaneously form disulfide bonds with other thiol-terminated molecules. Historically, these thiol-terminated biofunctional surfaces have been created by functionalizing a gold surface with thiol groups, followed by the introduction of alkylthiolates (R—SH) which order spontaneously and form a self-assembled monolayer, with the terminal end opposite the thiol functionalized with a biologically selective group, such as an enzyme or bio-substrate. An analyte can then be added, which selectively binds to the functionalized monolayer.
Self-assembled monolayers have been preferred due to the potential for the bulk substrate surface to impact the structure of the bio-molecule of interest. For example, proteins can be irreversibly denatured by interaction with hydrophobic or hydrophilic functionalized surfaces if such a monolayer is not used. Therefore, if the secondary, tertiary, or quaternary structure is of importance, immobilization directly on a surface is inadvisable.
The gold required for the introduction of thiol groups is typically applied using lithographic techniques, which are time consuming and expensive. A method for immobilization of bio-molecules on a surface without the intervening steps of gold application and self-assembled monolayer formation is desired.
In general, a robust, accurate method of attachment of nano-objects to a surface at precise locations is desired.